Lutropin (LH) and follitropin (FSH) are two anterior pituitary hormones that play key roles in the growth and development of the ovarian follicle. The LH and FSH receptors (LHR and FSHR, respectively) are both expressed in granulosa cells but in spite of structural and functional similarities between LH and FSH and between the LHR and the FSHR, the LH/LHR and FSH/FSHR pairs can have divergent effects on granulosa cells. Since at least some of these divergent effects are detectable when the LHR and FSHR are expressed in immature granulosa cells we hypothesize that they are due to the ability of these homologous hormone/receptor pairs to preferentially activate distinct signaling pathways in immature granulosa cells rather than to the expression of the LHR and FSHR in granulosa cells at different states of differentiation. We will use primary cultures of immature rat granulosa cells and adenoviral vectors to direct the expression of the LHR and FSHR and to direct and/or ablate the expression of other signaling proteins to identify the signaling pathways activated by each of these hormone/receptor pairs and to determine which of these pathways are responsible for the differential effects of FSH and LH on the induction of two classical markers of granulosa cell differentiation, aromatase and the endogenous LHR. The specific aims are as follows. (1) Characterize the signaling properties of the LHR and FSHR expressed in immature granulosa cells. (2) Determine the reasons why increasing densities of the LHR decrease the ability of FSH to induce markers of granulosa cell differentiation. (3) Determine if the differential effects of the FSH/FSHR and LH/LHR pairs on the induction of markers of granulosa cell differentiation are due to the hormones and/or the receptors. (4) Determine which of the pathways identified in Aim 1 are responsible for the differential effects of the FSH/FSHR and LH/LHR pairs on the induction of markers of granulosa cell differentiation.